Lamp and mount



Nov. 8, 1960 N. c. BEEsE LAMP AND MOUNT Filed July 2,' 1958 FIG. I.

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United States Patent LAMP AND MOUNT Norman C. Beese, Verona, NJ., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed July 2, 1958, Ser. No. 746,137

Claims. (Cl. 313-109) This invention relates to discharge devices and, more particularly, to low-pressure, positive-column, mercurydischarge devices, particularly of the fluorescent type and mounts therefor.

Low-pressure, positive-column, mercury-discharge devices, and especially fluorescent lamps, display a marked tendency to form -spots and other blackening at the ends of the envelope proximate the axial projections of the lamp electrodes. These so-called anode spots apparently are primarily comprised of barium from the cathodes and sputtered lead material such as nickel, which amalgamates with the mercury contained within the device to form a blackened spot. Such spots usually manifest themselves after the lamp has been operated for some time and then become increasingly pronounced during the remainder of the life of the lamp. Such discolorations are objectionable from the appearance aspects as well as cutting `down somewhat on the emitted light.

It is the general object of this invention to avoid and overcome the foregoing and other diiculties of and objections to prior-art practices by the provision of an improved mount structure, which when incorporated into a discharge device drastically inhibits the first appearance of so-called anode spots.

It is another object to provide speciiic mount -and lamp constructions incorporating specific materials for the purpose of inhibiting the formation of anode spots.

The aforesaid objects of the invention, and other objects which will become apparent as the description proceeds, are achieved by providing van improved mount structure and a discharge device incorporating such improved mount structure, wherein the electrode coils have positioned opposite either end thereof individual metallic shields. The shields are electrically connected to and supported by the lead conductors which support the electrodes. These shields are so positioned and conformed as to intersect completely the axial projections of the Velectrode coils and 'at least the inner surfaces of the shields, that is 4those surfaces which face the electrode coils, carry thereon a porous, amorphous layer of carbon, or boron, or a mixture thereof.

For a better understanding of the invention, reference should be had to the accompanying drawing wherein:

Fig. 1 is an elevational view, partly in section, of a iluorescent lamp incorporating the improved electrode mount structure;

Fig. 2 is a fragmentary enlarged elevation showing details of the improved mount structure as incorporated into the iluorescent lamp;

Fig. 3 is a sectional view taken on the line III-III in Fig. 2 in the direction of the arrows; l

Fig. 4 is a perspective View of the improved mount structure incorporating the additional coated shields.

The invention is usually employed in conjunction with fluorescent lamps, that is low-pressure, positive-column mercury-discharge devices which carry a coating of phosphor material on the interior surface of the lamp 'en- ICC velope and hence it has been so illustrated and willbe so described. It should be understood, however, that the invention is equally applicable to such devices which do not carry a phosphor coating on the interior surface of the envelope, but are intended to be used as ultraviolet sources, for example. In addition, the most common type of iluorescent lamp is the 40 w. T12 and this type of lamp will be considered in detail in the following description, although the principles of the invention are equally applicable to any type of uorescent lamp.

With specific reference to the form of the invention illustrated in the drawing, the numeral 10 in Fig. l illustrates generally a 40 w. T12-type fluorescent lamp comprising a tubular vitreous envelope 12 which is normally fabricated of the usual soda-lime-silica glass, having mounts 14 sealed into either end thereof as is customary. Each mount comprises a vitreous portion 16 sealedto one end of the envelope 12 with lead conductors 18 sealed therethrough and supporting at their inwardlyextending extremities refractory metal coils 20, which are normally fabricated of tungsten for example. These coils 20 are formed of a plurality of coil turns wound about an axis and are normally of a coiled-coil or a triple-coil construction, such constructionsV being well known. Contained within the turns of the inner coil or coils is a iilling of electron-emitting material 22. In the preferred embodiment, the axis of each of the electrode coils 2.0 yis disposed substantially perpendicular with respect to; the tubular axis of the envelope although if desired the coils may be disposed at other orientations with respect to the tubular axis of the lamp envelope 12.

The electron-emitting materials yas are normally used in fluorescent lamps are well known and comprise a mixture of alkaline-earth oxides which may have other materials such as zirconia `added thereto. The primaryl constituent of such electron-emitting materials normally is barium oxide and it is customary to include with `the barium oxide limited amounts of calcium oxide and strontium oxide. As a specific example, the electronemitting material comprises a mixture of 55% by weight barium oxide, 5% by weight calcium oxide and 40% by weight strontium oxide and there may be incorpoyrated an additive such as 0.9% by weight of zirconia, if

desired. This specific electron-emitting material is given only by way of example and many other mixtures nare possible. As noted hereinbefore, however, barium oxide is normally used in such electron-emitting materialsf Electrical connection for the lead conductors18'is effected by contact pins 24 which project from the supporting base caps 26 at either end of the lamp. The envelope 12 has coated on its interior surface a phosphor material 2.8 and the envelope also contains a sm-all filling of argon or other inert, ionizable gas `at a pressure of about 3 mm., for example, in order to facilitate starting. Other starting gases and other starting ,gas Y ll pressures can be used, as is well known. Also contained wi-thin the envelope -is a small charge of mercury 30, as is customary. The phosphor material 28 can comprise any of the well-known phosphors as are normally used with iluorescent lamps, specific examples beingzinc vsilicate activated by manganese or any of the well-known, so-called halophosphate phosphors. y

In accordance with the present invention, additional shields 32', as shown in expanded view in Figs. 2 and 3 and in perspective View in Fig. 4, are electrically connected to each of the lead conductors 18 by shield support wires 34. Preferably the support wires 34 are spotwelded to the lead conductors 18, although they can be t conformed as to intersect completely the axial projections of each of the coils 20. As a specific example, each of the coils 20 has a barrel length of l1 mm. and a maximum diameter of 0.065 inch.v In their preferred form the shields are formed as flat metal discs having a diameter of approximately one-quarter inch. Preferably each of the shields 32 is oriented in a perpendicular fashion with respect to the axes of the coils 20 in order to insure that the axial projections of the coils 20 are completely intersected by the shields and as a specific example the spacing between each of the shields and the ends of the coils is one-eighth inch. The preferred shield material is nickel although other metals such as molybdenum or chrome-plated iron can be substituted for the nickel if desired. The size and configuration of the shields 32 can be varied and they can be made square, oblong or rectangular if desired. The orientation of the shields 32 with respect to the coils 20 as well as the spacing therebetween can be varied, provided the shields completely intersect the axial projections of the coils 20.

Coated on at least the inner surfaces of the shields 32, that is the surfaces which face the coils 20, is a porous, `amorphous layer 36 of boron, or carbon, or mixtures thereof. Any mixtures of boron and carbon are suitable and an example is equal parts by weight. Desirably the entire shield surfaces are coated with the amorphous material as specified. The term amorphous as u sed herein and as generally used in the art refers to the lack of any clearly-defined X-ray diffraction pattern as is obtainable for the specified materials. The state of division of the specified materials is not critical provided they can be classed as amorphous and normally the average particle size of the specified materials will fall within the colloidal range of from 1 to 100 millimicrons.

After the support wires 34 are atiixed to the shields 32, the amorphous material or materials as specified are desirably coated onto the shields with a suitable binder material which can be volatilized after coating. As a specific example, a suitable coating composition cornprises 2 grams of amorphous carbon or boron or mixtures thereof admixed with cc. of butyl acetate having included therewith 2% by weight of nitrocellulose. This admixture is milled to form a homogeneous suspension with which the shields 32 are sprayed. Thereafter the coated shields are dried in air to allow the butyl acetate to volatilize and the shield support wires 34 are then either welded or clamped to the lead conductors 18 of the mount 14. As a specific example, the layer 36 has a thickness of about one mil and this thickness can be varied considerably. It is not necessary to volatilize the nitrocellulose binder from the coated amorphous material before the mounts 14 are incorporated into the fluorescent lamp envelope 12 since the small amount of binder material will be substantially volatilized during the usual lamp exhaust process.

In the mount 14 as shown in Fig. 4, the shields 32' are coated with the porous amorphous layer 36 and are affixed to the lead conductors 18 which carry the coil 20. The electron-emissive material coated onto the coil 20 is not treated, that is, it has not been heated to convert the barium carbonate and other alkaline-earth carbonates to the oxides, as is required to render the material electron emissive. After fabrication as shown in Fig. 4 the mounts 14 are sealed into either end of the phosphorcoated envelope 12 in accordance with the usual practices. The envelope is then exhausted, the electrodes are treated by passing a current therethrough to convert the barium carbonate and other alkaline-earth carbonates, if used, to the oxides. The envelope 12 is again exhausted, the starting gas and mercury charge inserted, and the tubulation tipped off. The base caps 26 are then affixed to the ends of the envelope 12. The foregoing fabrication procedures are customary in the art. During the exhausting procedure,V ih@ ellVelOPe 12 is heated to a temperature of approximately 450 C. and this will substantially volatilize the nitrocellulose binder material which is included in the layer 36 of the porous, amorphous material as specified.

In the usual fluorescent lamp, approximately 20% of the lamps will display some anode spot formation after approximately 500 hours of operation and after 1500 hours of operation, as much as 60% of the lamps may display anode spots. In control tests, lamps incorporating the coated shields as specified displayed substantially no formation of anode spots even after 5000 hours of operation. In further control tests, some lamps were provided with shields as specified hereinbefore but without the shield coating of porous, amorphous material. The presence of the shields per se without the coating material as specied inhibits to some degree the first formation of anode spots, but the improvement is only nominal. Additional lamps were provided with uncoated nickel shields at one electrode and with coated shields, as specified, at the other electrode. At the end of 2000 hours operation, only the ends which were provided with the coated shields remained free of the anode spots.

Apparently the barium component of the emissive material and some of the lead material is driven from the electrodes and leads either by ion bombardment, or by evaporation, or both and is directed to the portions of the envelope wall proximate the axial projections of the coils 20. There are also indications that the deposition of the barium and lead material is a two-step process, wherein sputtered or evaporated material rst deposits on the lead extremities of the coil. Thereafter the ion bombardment which is realized at the electrodes during the lamp operation causes barium and some of the lead material to be knocked from the leads and to be directed toward the envelope wall. The amorphous boron, or carbon, or mixtures thereof have a very light atomic weight and density and appear to act similar to a feather pillow or cushion with respect to the ion bombardment. Thus the very high velocity ions appear to expend their energy penetrating the porous, amorphous coating 36 and are not able to knock off any barium which might have been deposited onto the shields or any of the metallic base material of which the shields 32 are formed. By virtue of the electrical connection between the leads 18 and the shields 32, the shields are essentially maintained at the electrical potential which is used to operate the lamp 10. Sputtered or evaporated barium appears to be attracted to the shields 32' by virtue of their charged nature and upon striking the shields, this sputtered or evaporated material is embedded in the porous, amorphous coating 36 which serves to insulate it against any further ion bombardment as encountered during lamp operation. It should be noted that while boron and carbon are equally effective as a cushion, boron is preferred inasmuch as it is much easier to degasify, thereby simplifying lamp manufacture.

It will be recognized that the objects of the invention have been achieved by the provision of an improved mount structure and an improved discharge device wherein the formation of anode` spots on the envelope of such a device is inhibited. In addition, specific mount and lamp constructions incorporating specific materials have been provided, in order to inhibit the formation of anode spots.

While best-known embodiments have been illustrated and described in detail, it is to be particularly understood that the invention is not limited thereto or thereby.

I claim:

1. A mount structure for a low-pressure, positivecolumn, mercury-discharge device comprising, a refractory metal coil formed of a plurality of coil turns wound about an axis, an unactivated electron-emissive material comprising barium carbonate carried within the turns of said coil, spaced leads electrically connecting to and supporting said coil therebetween, individual metallic shields electrically connecting to one of each of said leads and supported thereby in spaced relationship from said coil, said shields completely intersecting the axial projections of said coils, and said shields carrying thereon a porous amorphous layer of at least one of the group consisting of carbon and boron.

2. A mount structure for a fluorescent lamp comprising, a refractory metal coil formed of a plurality of coil turns Wound about an axis, an unactivated electronemissive material comprising barium carbonate carried within the turns of said coil, spaced leads electrically connecting to and supporting said coil therebetween, individual metallic shields electrically connecting to one of each of said leads and supported thereby in spaced relationship from said coil, one surface of each of said shields facing said coil and completely intersecting the axial projection of said coil, and at least the surfaces of said :shields facing said coil carrying thereon a porous amorphous layer of at least one of the group consisting of carbon and boron. v

3. A mount structure for a uorescent lamp comprising, a fractory metal coil formed of a plurality of coil turns wound about an axis, an unactivated electronemissive material comprising barium carbonate carried Within the turns of said coil, spaced leads electrically connecting to and supporting said coil therebetween, individual metallic shields electrically connecting to one of each of said leads and supported thereby in spaced relationship from said coil, one surface of each of said shields facing said coil and completely intersecting the axial projection of said coil, and at least the surfaces of said shields facing said coil carrying thereon a porous amorphous layer of boron.

4. A mount structure for a fluorescent lamp comprising, a refractory metal coil :formed of a plurality of coil turns Wound about an axis, an unactivated electronemissive material comprising barium carbonate carried within the turns of said coil, spaced leads electrically connecting to and supporting said coil therebetween, individual metallic shields electrically connecting to one of each of said leads and supported thereby in spaced relationship from said coil, one surface of each of said shields facing said coil and completely intersecting the axial projection of said coil, and at least the surfaces of said shields facing said coil carrying thereon a porous amorphous layer of carbon.

5. A mount structure .for a fluorescent lamp comprising, a refractory metal coil formed of a plurality of coil turns wound about an axis, an unactivated electronemissive material comprising barium carbonate carried within the turns of said coil, spaced leads electrically connecting to and supporting said coil therebetween, individual disc-like metallic shields electrically connecting to one of each of said leads and supported thereby in spaced relationship from said coil, one surface of each of said shields facing said coil and completely intersec-ting the axial projection of said coil, and at least the surfaces of said shields facing said coil carrying thereon a porous amorphous layer comprising at least one of the group consisting of carbon and boron.

6. A positive-column, low-pressure, mercury-discharge device comprising, a sealed tubular vitreous envelope, a charge of mercury and an inert ionizable gas contained within said envelope, a pair of mount structures posi- -tioned within said envelope at either end thereof, and each of said mount structures comprising: a refractory metal coil formed of a plurality of coil turns Wound about an axis, an electron-emissive material comprising barium oxide carried within the turns of said coil, spaced leads electrically connecting to and supporting said coil therebetween, individual metallic shields electrically connecting to one of each of said leads and supported thereby in spaced relationship `from said coil, said shields completely intersecting the axial projections of said coil, and

j said shields carrying thereon a porous amiphouslyer of at least one of the group consisting of carbon and boron.

7. A fluorescent lamp comprising, a sealed tubular vitreous envelope, phosphor material coated on the interior surface of said envelope, -a charge of mercury and an inert ionizable gas contained within said envelope, a pair. of mount structures positioned within said envelope at either end thereof, and each of said mount structures comprising: a refractory metal coil formed of a plurality of coil turns wound about an axis, an electron-emissive material comprising barium oxide carried within the turns of said coil, spaced leads electrically connecting to and supporting said coil therebetween, the axis of said coil disposed substantially perpendicular with respect to the tubular axis of said envelope, individual metallic shields electrically connecting to one of each of said leads and supported thereby in spaced relationship from said coil, one surface of each of said shields facing said coil and completely intersecting the axial projection of said coil, and at least the surfaces of said shields `facing said coil carrying thereon a porous amorphous layer comprising at least one of the group consisting of carbon and boron.

8. A fluorescent lamp comprising, a sealed tubular vitreous envelope, phosphor material coated on the interior surface of said envelope, a charge of mercury and an inert ionizable gas contained within said envelope, a pai-r of mount structures-positioned within said envelope at either end thereof, and each of said mount structures comprising: a refractory metal coil formed of a plurality of coil turns wound about an axis, an electron-emissive material comprising barium oxide carried Within the turns of said coil, spaced leads electrically connecting to and supporting said coil therebetween, the axis of said coil disposed substantially perpendicular with respect to the tubular axis of said envelope, individual metallic shields electrically connecting to one of each of said leads and supported thereby in spaced relationship from said coil, one surface of each of -sad shields facing said coil and completely intersecting the axial projection of said coil, and at least the surfaces of said shields facing said coil carrying thereon a porous amorphous layer of boron.

9. A fluorescent lamp comprising, a sealed tubular vitreous envelope, phosphor material coated on the interior surface of said envelope, -a charge of mercury and an inert ionizable gas contained Within said envelope, a pair of mount structures positioned within said envelope at either end thereof, and each of said mount structures` comprising: a refractory metal coil formed of a plurality of coil turns wound about an axis, an electronemissive material comprising barium oxide carried within the turns of said coil, spaced leads electrically connecting to and supporting said coil therebetween, the axis of said coil disposed substantially perpendicular with respect to the tubular axis of said envelope, individual metallic shields electrically connecting to one of each of said leads and supported thereby in spaced relationship from said coil, one surface of each of said shields facing said coil and completely intersecting the axial projection of said coil, and at least the surfaces of said shields facing said coil carrying thereon a porous amorphous layer of carbon.

10. A iluorescent lamp comprising, a sealed tubular vitreous envelope, phosphor material coated on the interior surface of said envelope, a charge of mercury and an inert ionizable gas contained within said envelope, a pair of mount structures positioned Within said envelope at either end thereof, and each of said mount structures comprising: a refractory metal coil formed of a plurality of coil turns wound about an axis, an electronemissive material comprising barium oxide carried within the turns of said coil, spaced leads electrically connecting to and supporting said coil therebetween, the axis of said coil disposed substantially perpendicular with respect to the tubular axis of said envelope, `individual `ydisc-1ke metallic shields electrically connecting to one of each of said leads and supported thereby in spaced vrelationship from said coil, one surface of each of said shields facing said coil and completely intersecting the axial projection of said coil, and at least the surfaces of said shields facing said coil carrying thereon a porous amorphous layer comprising at least one of the group consisting of carbon and boron.

References Cited in the flle of this patent UNITED STATES PATENTS Knowles May 7, 1940 Besser Oct. 14, 1947 Toorks Dec. 30, 1947 Penon Jan. 21, 1958 

